Submarine Record of Disastrous Earthquakes at a Strain Partitioned Transpressional Boundary: NSF RAPID Response of the Enriquillo-Plantain Garden Fault, Jamaica Passage

As part of an NSF RAPID response to the Mw7.2 August 14, 2021, Haiti earthquake, we conducted marine geophysical surveys within the Jamaica Passage and offshore Kingston sections of the Enriquillo-Plantain-Garden Fault (EPGF) transpressional plate boundary. Across the Jamaica Passage, the EPGF follows a 2.5-3 km deep trough inherited from early Cenozoic Caribbean tectonics. The trough contains from E to W, the Matley, Navassa and Morant basins, which were our survey areas in January 2022. Here we collected 50 high-resolution multichannel seismic-reflection profiles (MCS), 30 heat flow measurements and 47, 0-5 m long gravity cores from the R/V Pelican. With these data we assess fault partitioning and rupture evolution of faults along the EPGF, in order to evaluate seismic risk for the heavily populated regions of Southeastern Jamaica and Southwestern Haiti. This survey builds upon prior work from French studies and a 2010 NSF Haiti RAPID. Initial interpretation of the MCS reveals evidence of substantial N-S shortening along the EPGF consistent with a transpressional regime that is inverting earlier extension of the crust. The N-S shortening is generally expressed as thrust-folding with southward vergence that is shifting the surface trace of the EPGF southward. Although the shortening is recognized along the land portions of the EPGF in both Haiti and Jamaica, it is notably absent from the westernmost Morant basin. Among the new and exciting findings is the EPGF forms a ~23 m high scarp in the Morant Basin; this observation provides evidence that the fault is active and likely experienced recent large earthquake ruptures. Sediments are mainly composed of pelagic calcareous oozes which dominate the sand component and iron rich clayey silts from erosion of basalt outcrops on fault ridges. Initial results from short-lived radioisotopes show sedimentation rates of 10 cm/1000 years. These slow rates are consistent with a carbonate setting dominated by pelagic sedimentation. We identify the sedimentary signatures of three earthquakes with recurrence intervals of ~1000 years based on C-14. One of these event deposits was dated at 2000 cal years BC and observed for over 110 km along the plate boundary, suggesting a rupture across the entire Jamaica Passage and consistent with the formation of scarps during large ruptures